linux-kernel - Re: [PATCH 2/3] Security: Implement disablenetwork semantics. (v4)

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Date:	Mon, 11 Jan 2010 01:21:08 +0000 (UTC)
From:	daw@...berkeley.edu (David Wagner)
To:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] Security: Implement disablenetwork semantics. (v4)

Michael Stone  wrote:
>Pavel's position is that disablenetwork is likely to permit some attacker
>somewhere to deny network access to some setuid app some day in a way that
>violates some security policy.
>
>He has mentioned specific concern over scenarios like:
>
>   Alice configures PAM auth to 'fail open' by checking login credentials
>   against a restrictive LDAP server and, if the server is unavailable, against
>   a very permissive files database.
>
>   Alice updates her kernel to a version with disablenetwork.
>
>   Mallory calls disablenetwork, calls su -, and vanquishes all.
>
>My position is that better isolation facilities like disablenetwork will
>prevent far more grievous security faults than they (theoretically) cause.
>
>What is your perspective on the matter?

I agree with you.  As I've mentioned before, I think it's an unconvincing
objection.  If Alice sets such a poorly thought-out security policy,
then there are probably many other ways to attack the system, even if
you don't introduce disablenetwork.  (Example atttack #1: Use rlimit
to set the number of file descriptors that can be opened very low, then
call su -.  Example attack #2: DOS the LDAP server, and then call su -.
There are probably many more.)

But it's also true that it's possible to achieve many of the benefits
of disablenetwork in a way that avoids introducing the potential risks
that Pavel is concerned about.  If that's the political compromise
that it takes to get disablenetwork into the kernel, that's still a
step forward.  It'd be better than what we have today.
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